The present invention relates to a system for processing data derived from reading coded labels attached to merchandise items during a checkout operation. In order to increase the speed of the checkout operation, optical scanner devices have been incorporated into checkout counters for reading data encoded indicia on labels affixed to the purchased merchandise items. Movements of the merchandise items past the scanner device results in the scanner device reading the encoded indicia labels. To control the operation of the scanner device, detecting means have been positioned in the path of movement of the merchandise items to operate the scanner device in accordance with the position of the merchandise items with respect to the scanner device. Thus, a first or enter detector means positioned upstream of the scanner device will turn on the scanner device for operation upon detecting the presence of a merchandise item upstream of the scanner device, while a second or exit detector means located downstream of the scanner device will turn the scanner device off upon detecting the presence of the merchandise item downstream of the scanner device. In actual operation, it has been found that the checkout operator in moving a merchandise item past the scanner device will sometimes lift the item above the detectors so as not to trip one or the other detector means during the checkout operation. When this occurs, the operator is notified by signal lights localed in the checkout counter or by audio tones to repeat the read operation. In repeating the checkout movement, the operator will sometimes trip both detectors or one of the detectors in returning the merchandise item to a start position prior to moving the items past the scanner device in the proper direction, resulting in the mis-operation of the scanning device. It is therefore an object of this invention to provide an optical scanner control system which will efficiently utilize the scanner device irrespective of the movement of the merchandise items past the scanner device. It is a further object of this invention to provide a control system for operating the scanner device in a manner to force a prescribed mode of operation by the checkout operator to maximize the performance of the scanning unit.